The Anaesthesia Machine

Question 1

The Anaesthesia Machine/ Boyle’s Machine

Answer 1

2 principal functions:
Delivers gases to the patient (oxygen (100%), medical air (21%), nitrous oxide and volatile anaesthetic agents)
Provides a means to manually ventilate the patient under positive pressure (via a connected bag and/or an integrated automatic ventilator)
Modern machines have integrated patient monitors

Question 2

Basic parts of the machine

Answer 2

1. GAS SUPPLIES UNDER PRESSURE
   Piped medical gases from a central supply
   Backup cylinders on the machine. ALSO there is an Emergency O2 flush
2. GAS FLOW CONTROLS
   Flow meters or rotameters
3. VAPORISERS
   Convert volatile anaesthetic agents into gaseous form
4. THE BREATHING CIRCUIT
   Connects machine to airway of patient (mask/ETT/SGA)
5. VENTILATION SYSTEMS
   Reservoir bag for manual ventilation
   * Automatic ventilator

Question 3

GAS SUPPLIES UNDER PRESSURE: O2

Answer 3

Stored in liquid form in giant external tank(s) periodically filled=> converts to gaseous form and enters central pipeline to machine.
Also stored in a back-up cylinder.
Oxygen piping is colour coded white;
Oxygen cylinders are black with white shoulders

Question 4

GAS SUPPLIES UNDER PRESSURE: N2O

Answer 4

Commonly used as a carrier gas to augment anaesthesia
Stored as gas in cylinder
Cylinder and piping colour: royal blue

Question 5

GAS SUPPLIES UNDER PRESSURE: Other gases on wall

Answer 5

Vacuum= Yellow

Compressed Air= Grey

Question 6

Gas piping from wall outlets connecting to machine

Answer 6

Blue—Nitrous Oxide
White—Oxygen
Black—Clean medical air (21% oxygen in 78% nitrogen)

Question 7

Flowmeters

Answer 7

Gas enters the anaesthesia machine under high pressure (O2, N2O and medical air)
This is stepped down to safe pressure by valves
Individual flow controls for each gas (modern machines: may be virtual / electronic)
Safety interlink prevents N2O from being given alone (oxygen always opens as well)
Gas flows and concentrations mixed as needed by anaesthetist
Oxygen usually mixed with either N2O (to augment anaesthesia) or air (to control SATS and Hyperventilation(CO2) during anaesthesia
O2 is given alone @100% for pre-oxygenation prior to intubation.

Question 8

Vaporisers

Answer 8

Convert volatile anaesthetics from liquid into gaseous form, then delivered into the gas mixture given to the patient.
Each volatile agent has a specific vaporiser and is colour-coded
Require special fillers with specific shapes.
ANAESTHETIC’S BACK-BAR INTERLOCKS SO ONLY ONE VAPORISER CAN BE GIVEN ONE AT A TIME.
halothane (RED), isoflurane (PURPLE), sevoflurane(YELLOW) and desflurane (BLUE).

Question 9

Vaporiser fillers

Answer 9

May be be metal or plastic keyed fillers or funnel-filler adapters.
Specific for each agent
Colour-coded as the same agent
One side fits specifically on the correct vaporiser bottle, the other fits specifically into the correct corresponding vaporiser.

Question 10

Breathing circuits: The Circle System

Answer 10

The CIRCLE SYSTEM is used on modern anaesthesia machines AND is used as a humidifier.
It consists of piping (tubing) with unidirectional valves
Gas flows from the machine into the inspiratory limb to the patient
The patient exhales via the expiratory limb
The system contains a carbon dioxide absorption system.
HAS POP OFF VALVE

Question 11

Soda-Lime

Answer 11

Soda-Lime granules absorb exhaled carbon dioxide in the Circle System and as such, low flows of gas can be used which is economical.
CO2 reacts with soda-lime to form heat and moisture=> prevents drying out of the patient’s airway
The soda lime changes colour when it is exhausted FROM WHITE TO PURPLE.

Question 12

The Ayre’s T-Piece (Paediatric Jackson-Rees Circuit)

Answer 12

Valve free, reservoir bag is open

No CO2 absorption so requires a minimum gas flow to wash out CO2

Question 13

Heat Moisture Exchange Filters (HMEFS)

Answer 13

Warm and humidify gases delivered to patient
Single-use, changed for new patients
Placed at end of ETT or mask, closest to patient connected to rest of circuit
DOES NOT FILTER BACTERIA

Question 14

The Reservoir Bag

Answer 14

Used for manual ventilation when adjustable valve
During spontaneous breathing when valve is closed, it is used to monitor resp efforts as it can provide PEEP OR used to check the circuit for leaks

Question 15

Self-Inflating Resuscitators (AmbuBag)

Answer 15

Are free-standing, self-inflating essential equipment
Used as backup ventilation device
Are also used to transport patients
Connector for oxygen
Patients can also breathe spontaneously with these